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The Bathroom is the first of Jean-Philippe Toussaint's novels, but it already bears many of the hallmarks of his later work, specifically a disaffected male narrator, not entirely passive but pretty much just going with the flow, travelling (fairly aimlessly) abroad, in a narrative that meanders through the mundane.
The three-part novel is presented in short, numbered paragraphs; an epigraph -- (almost) Pythagoras' theorem, "The square of the hypotenuse is equal to the sum of the squares of the other two sides" -- suggests a mathematical foundation, though the numbers of the paragraphs in each side/section don't work out.
The narrator lives in Paris with his girlfriend, Edmondsson, and at the beginning of the novel has beaten a slow retreat to the bathtub, finding it a congenial place to while away the hours.
First she, then even he wonder whether this is such a good idea, and eventually:

Seated on the edge of the bathtub, I was explaining to Edmondsson that perhaps it was not very healthy, at age twenty-seven going on twenty-eight, to live more or less shut up in a bathtub.
I ought to take some risk, I said, looking down and stroking the enamel of the bathtub, the risk of compromising the quietude of my abstract life for ... I did not finish my sentence.

And so: "The next day I left the bathroom."
But does it get him anywhere ?
He seems to remain in abstract-life mode for the duration, even as he shuffles through the day-to-day.
There's a bit of activity in the apartment, as Edmondsson has hired some painters -- Polish artists exhibiting at the gallery she works at, looking to make some extra cash -- but they pretty much just hang around in the kitchen, since Edmondsson hasn't bought paint yet.
The narrator offers up a variety of thoughts and recollections, such as when they had met the previous tenants of the apartment, but very little happens.
Readers aren't treated to descriptions of watching the paint dry, but there is, for example, a chapter discussing: "the two ways to watch rain fall from behind a pane of glass".
Abruptly, the narrator flees -- to Venice, not his bathtub.
As if a change of scenery might help.
But his rut is so deep that it hardly seems to matter where he is.
Again, not much happens, though eventually Edmondsson comes to visit.
There is one scene of unexpected violence -- a striking bull's-eye -- but even that only shakes him out of his reveries so far.
Still, eventually he heads on home, only to have the story come full circle (and a bit more).
Toussaint's laconic tone, and the sum of the observations does make for a surprisingly rich novel.
Only occasionally does the narrator offer deeper insights -- his love of Mondrian, for example, in whose paintings even: "immobility is immobile" (which he finds reassuring), while Edmondsson of course finds him: "a crushing bore" -- but it's the banalities and everyday trivialities, like that dripping bag of octopus one of the Poles brings over, that make the novel.
The narrator at one point claims: "Suffering was the ultimate, the only confirmation of my existence", but it feels almost out of character, like a sudden, hopeful cry, rather than recognition of a deeper truth about himself.
There's little suffering going on, and he shies away from most other confirmations of his existence.
What few there are seem almost mistaken: among the things that move him to get out of his bathtub (twice !) are invitations from the Austrian embassy, but he doesn't know anyone there and can't explain why they should invite him; they are sort of phantom-invitations, confirmation not so much of his real existence but of a fake and almost illusory one.
For a novel that loops its way from one lethargic retreat to the next (and despite the clever ending there
seems little hope this guy won't wind up in the bathtub yet again and yet again) and in which very little happens,
The Bathroom is pleasantly entertaining; the fact that it only goes on for a hundred pages presumably also helps.
Good, odd fun.